Method for producing cellulosic forms

ABSTRACT

Process for producing formed cellulosic articles, such as fibers, filaments, sheetings, membranes or tubes, comprising a) extruding a solution of cellulose in an aqueous amine oxide, particularly N-methylmorpholine N-oxide, through an extrusion die via an air gap and coagulating the formed article in an aqueous precipitation bath containing amine oxide, and b) passing the formed article through at least one washing stage for removing residual amine oxide from the article, characterized in that the liquor of the precipitation bath in the precipitation stage and/or the washing liquor of the washing stage(s) is treated with ultra-violet radiation. In this manner the formation and growth of coatings, films and slime deposits caused by microorganisms is avoided on parts of the plant which come into contact with said liquors containing the amine oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 USC §371 and claimsthe priority of International Patent Application No. PCT/DE99/02976filed Sep. 14, 1999, which in turn claims priority of German PatentApplication No. 198 42 556.2 filed Sep. 17, 1998.

FIELD OF THE INVENTION

The invention relates to a process for producing formed cellulosicarticles, such as fibres, filaments, sheetings, membranes or tubes,comprising a) extruding a solution of cellulose in an aqueous amineoxide, particularly N-methylmorpholine N-oxide, through an extrusion dievia an air gap and coagulating the formed article in an aqueousprecipitation bath containing amine oxide, and b) passing the formedarticle through at least one washing stage for removing residual amineoxide.

BACKGROUND OF THE INVENTION

While the precipitation bath usually has concentrations ofN-methylmorpholine N-oxide (NMMO) from 10 to 25% by mass andtemperatures from 0 to 20° C., in the subsequent washing stages the NMMOcontent of the washing liquors is decreased to nearly 0% at temperaturesup to 80° C. It is known that these NMMO-containing liquors arecharacterized by a partially very strong growth of microorganisms. Thesebiological substances are sustantially bacteria and fungi and causeconsiderable difficulties with the processing by the formation of slimeaggregates and biofilms. The function of parts of the production plantcan be impaired by clogging of pipes, filters, pumps etc. up to theirtotal breakdown. A mechanical cleaning of the washing and precipitationbath systems is very expensive due to the marked adhesion of thepolymeric slime substances to all the surfaces and results in unwantedinterruptions of the production process.

From WO 96/18761 a process is known in which the biological substancesin the baths are degraded by using usual oxidants, such as e.g. hydrogenperoxide, peracetic acid, ozone or chlorine dioxide. With this method itmust be assured by an expensive mechanism that these oxidants arecompletely disposed before recycling the NMMO into the dope productionstage.

According to the process specified in WO 97/07137 a microbicidal agentis added during or after the regeneration of solutions containing amineoxide in order to avoid formation of films in the apparatus. In thiscase likewise the disadvantage exists that the added substance or itsdegradation products are concentrated in the NMMO cycle of the processand cause unwanted effects in the individual process steps. Theconsequences for the thermal stability of the NMMO and the accompaniedsafety risk must be particularly critically considered.

From WO 97/07108 and WO 97/07138 the UV treatment of amine oxidecontaining solutions is known with the aim to destroy theN-nitrosomorpholine formed during or after the oxidation ofN-methylmorpholine (NMM) to NMMO. The UV treatment is restricted to theregeneration of the precipitation bath for the purpose of reusing theregenerated NMMO for preparing the dope.

SUMMARY OF THE INVENTION

It is the object of the invention to avoid the formation and growth ofthe coatings, films and slime aggregates formed by microorganisms in theparts of the plant having contact with the MMO containing liquors andthe impairment and operating troubles caused thereby. Particularly theabove-mentioned process should not require frequent cleaning of theplant even in a continuous operation. Furthermore, it should berefrained from using chemical substances in order to avoid the problemsof their monitoring and, if required, their re-separation accompaniedtherewith. Further advantages can be gathered from the followingspecification.

With the process specified at the beginning, according to the inventionthese objects are achieved in that the liquor of the precipitation bathin the precipitation stage and/or the washing liquor of the washingstage(s) is treated by ultra-violet radiation. Surprisingly it has beenfound that the microorganisms developing in liquors containing amineoxide, particularly NMMO, which microorganisms result in the unwanteddeposits, are deactivated by the UV radiation or their DNS(deoxyribonucleic acid) is killed by a UV induced reaction. As a resultthe total germ number in the liquor is maintained low, and possiblecleanings of the plant are only necessary after substantially longeroperating periods.

According to the preferred embodiment of the process of the invention aultra-violet radiation of a wave length in the range from 200 to 280 nmis used. Especially the used UV radiation has a wave length of 254 nm:Conveniently this radiation is generated by a mercury low-pressure lampthe maximum intensity of which is at this wave length.

Preferably the UV treatment of the liquors of the washing stage(s) islimited to a temperature below 50° C. When operating with severalwashing steps in series the temperature of the washing liquor of thelast steps is often elevated above 50° C. in order to support washingthe amine oxide out of the formed articles. In these stages the UVradiation treatment can be omitted because the microorganisms cannotdevelop at these temperatures. On the other hand the growth of themicroorganisms is strongly inhibited at temperatures below 20° C. As theprecipitation baths are frequently maintained below this temperature theradiation can then be markedly reduced. As far as it is possible in thesubsequent washing stages to avoid temperatures between 20 and 40° C.,the radiation power can be reduced also in those stages.

Preferably the precipitation bath liquors or the washing liquors havinga Hazen Color Number Hz≦400 are subjected to the UV treatment. It hasbeen found that more intense colorings of the liquors reduce theefficiency of the UV treatment and require higher radiation powers. Theeffectivity of the UV treatment is ensured up to said Hazen ColorNumber. Consequently, suppressing the formation of colored side productsis also advantageous with the UV treatment of the precipitation bath andwashing liquors according to the invention aside from other reasons.

If with the process of the invention the precipitation bath and severalwashing stages are connected in series and comprise liquor cycles oftheir own, the cycle liquors of the precipitation bath and the firstwashing stage(s) are treated with UV radiation because these liquorsoffer comparatively favorable conditions (temperature, content oforganic substances) for the development of microorganisms. As the liquorfrom the last washing stage is passed to the precipitation bath oppositeto the movement of the fibres, it is repeatedly exposed to the UVradiation on this path. The UV radiation in a cycle can be carried outcontinuously or intermittently. It is possible to integrate the UVradiators in a simple manner also in already existing plants.

Preferably the cycle liquors are irradiated with a power in the rangefrom 0.1 to 1.0 Wh/l, especially with 0.5 Wh/l. The conditions for themicrobiological growth and the effectiveness of its combat by UVradiation are very different depending on the pH value, temperature,concentration of NMMO, oxygen introduction and light transmission (colornumber). The respective specific conditions can be taken into account byadapting the power and duration of the UV irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE shows a diagrammatic representation of a plant for carryingout the process of the invention with a precipitation bath and aconnected five-stage washing part.

The precipitation bath has an internal cycle for the bath liquor fromthe catch vat 1 ^(b) to the spinning vessel 1 ^(a) with a pump 1 ^(c), acooler 1 ^(d) and a UV radiator 1 ^(e). Spent precipitation bath iswithdrawn via line 1 ^(f) and passed to a cleaning stage 2. The cleanedprecipitation bath is concentrated in the stage 3. The formed NMMOconcentrate is used in the stage 4 for preparing the dope which ispumped to the spinnerets. The distillate formed in the stage 3 is fed aswashing liquor to the last washing stage 9.

The first washing stage 5 has an external washing liquor cycle 5 ^(a)with an UV radiator 5 ^(e). NMMO-containing washing liquor is passedfrom the cycle 5 ^(a) via a line 5 ^(b) to the catch vat 1 ^(b) Thesecond^(d) washing stage 6 is provided with an UV radiator 6 ^(e) in thesame manner as the first washing stage 5. The further washing stages 7,8and 9 have likewise external washing agent cycles 7 ^(a) 8 ^(a) and 9^(a), respectively, which differ from the cycles 5 ^(a) and 6 ^(a) inthat no UV radiator is arranged in them because the temperatures of thewashing agent is here maintained above 50° C. The path of the extrudedproducts through the plant is shown by a dashed line.

DETAILED DESCRIPTION OF THE INVENTION PRACTICAL EXAMPLE

In the plant shown in the FIGURE the UV radiators are operated with apower of 0.5 Wh/l circulated liquor. The total germ number wasdetermined in intervals of 2 days with samples from the precipitationbath by means of cultures (TTC Agar). The total germ number wascontinuously below 10⁵/ml. A cleaning was only necessary after 2 months.

COMPARATIVE EXAMPLE

With the same procedure as in the practical example, however without theUV irradiation, an increase of the total germ number to >10⁶/ml alreadyfound after 5 days inspite of a careful cleaning and disinfection.

What is claimed is:
 1. A process to avoid formation and growth ofcoatings, films and slime aggregates formed by microorganism in theproduction of formed cellulosic articles, such as fibres, filaments,sheetings, membranes or tubes, comprising a) extruding a solution ofcellulose in an aqueous amine oxide, particularly N-methylmorpholineN-oxide, through an extrusion die via an air gap and coagulating theformed article in an aqueous precipitation bath containing amine oxide,and b) passing the formed article through at least one washing stage forremoving residual amine oxide, characterized in that the liquor of theprecipitation bath in the precipitation stage and/or the washing liquorin the washing stage(s) is treated with ultra-violet radiation.
 2. Theprocess according to claim 1 wherein the ultra-violet radiation has awave length in the range from 200 to 280 nm.
 3. The process according toclaim 2 wherein the ultra-violet radiation has a wave length of 254 nm.4. The process according to claim 2 wherein the ultra-violet radiationis generated by a mercury low-pressure lamp.
 5. The process according toclaim 2 wherein the UV treatment is limited to the liquors of thewashing stage(s) having a temperature below 50° C.
 6. The processaccording to claim 1 wherein precipitation bath liquors or washingliquors having a Hazen color number Hz≦400 is subjected to the UVtreatment.
 7. The process according to claim 1 wherein the precipitationbath and several washing stages are connected in series and have liquorcycles of their own, characterized in that cycle liquors of theprecipitation bath and the first washing stage(s) are treated withultra-violet radiation.
 8. The process according to claim 1characterized in that power of the UV-radiation is in the range from 0.1to 1.0 Wh/l.
 9. A system for reducing unwanted microorganisms in liquorscontaining amine oxide, comprising: a precipitation bath; and a seriesof washing stages communicatively connected to each other and theprecipitation bath wherein the precipitation bath and at least one ofthe washing stages comprise a UV radiation source positioned forirradiating the washing liquor therein with ultra-violet radiation toreduce unwanted microorganisms in the washing liquor.
 10. The systemaccording to claim 9 wherein the ultra-violet radiation has a wavelength in the range from 200 to 280 nm.
 11. The system according toclaim 9 wherein the ultra-violet radiation has a wave length of 254 nm.12. The system according to claim 9 wherein the ultra-violet radiationis generated by a mercury low-pressure lamp.
 13. The system according toclaim 9 wherein the irradiation treatment is limited to the liquors ofthe washing stage(s) having a temperature below 50° C.
 14. The systemaccording to claim 9 wherein liquors in the precipitation and/or washingstages having a Hazen color number Hz≦400 is subjected to the UVtreatment.
 15. A method for reducing unwanted microorganisms in washingliquors containing amine oxide, comprising: irradiating washing liquorcontaining a N-methylmorpholine N-oxide in at least one washing stagewith ultra-violet radiation in a sufficient amount to effectively reduceunwanted microorganisms therein, the ultra-violet radiation having awave length in the range from 200 to 280 nm.